D. Mazia. DNA replication and chromosome condensation (as well as protein synthesis and a number of changes in membrane functions) may be turned on in unfertilized sea urchin eggs by a number of treatments: ammonia, nonelectrolyte media and trypsin-dithiothreitol. Scanning microscopy shows common changes of the cell surface with these treatments. The effects are interpreted as the removal of peripheral components of the membrane which should be accessible to chemical identification. For the chemical studies, a method of mass isolation of the cell surface complex has been developed. It is shown that these treatments turn on both histone synthesis and the phosphorylation of nucleosides even when no nucleus is present. Using the polylysine method of attaching cells to solid substrates, it has been possible to trace the fusion of egg and sperm from the first contact at the outer surface to the eruption of the sperm contents through the inner surface. F. Wilt. The studies on control of development have focussed on messenger RNA. It has been demonstrated that in activated sea urchin eggs the polyadenylate at the 3' end of a messenger RNA molecule is elongated by further addition of adenylate. A non-poly A containing mRNA, histone mRNA, has been isolated and its stability studied by chemical methods and by injection into living Xenopus oocytes. A new method for determination of intracellular nucleoside triphosphates has been developed. R. Strohman. These studies all relate to elementary questions of muscle growth and the regulation of muscle development. The findings may prove to be important to those interested, as we are, in growth defects, in developmental problems of muscle growth, and in ways of correcting these defects. Our new studies on the effects of electrical stimulation on myosin synthesis provide us with a good model for studying hypertrophy (why muscles grow when exercised) and therefore with a model with which to study atrophy and aging. Finally, our studies on cardiac cells and their growth responses may show us the way to develop a culture system for the study of damage and repair in heart muscle cells. BIBLIOGRAPHIC REFERENCES: Mazia, D. 1975. Microtubule research in perspective. Annals, N.Y. Acad. Sci. 253, 7-13. (Text Abridged)